RussellNewnham

Does anyone experience any detonation (and related timing retardation by the computer) with 11:1 comp ratios?

If so, is it only when the temp gets above 100 F.

I ask because I am just about to install AFR heads and 40 thou headgaskets on my 2001 C5 which will give 11:1 comp ratio.

I am told by several tuners in Australia, which is where I live, that this is very high for a two valve/cylinder engine and I may experience some problems with detonation. Hence, I may experience timing retardation well below peak power.

Octane rating will obviously effect this scenario. The octane rating in Aus is 98 RON, whereas it is 93 in the US (an average of the MON and the RON). I have been told that the two octane rating of the two fuels, i.e., 98 RON, and 93 (average of MON and RON) are equal,

Does anyone have any input/knowledge here please ?

I would prefer to not pull off the heads again and change back to standard head gaskets because of loss of power resulting from excessive retardation if possible.

ChocoTaco369

if you're gonna spend all that money on a head install, you may as well buy some pistons to lower your compression ratio while you're at it. pistons are what, 500 bucks? a small price to pay to ensure long engine life and pick up some power while you're at it, IMO.

SiL3NtXWS6

iTrader: (17)

You will be fine. I am at 11:3:1 CR in Texas heat on my 408.

It's all in the tune.

02RedHawk

iTrader: (17)

What cam are you running? We really need to know your DCR instead of your SCR.

RussellNewnham

Am going to run a 224 224 0.581 114.

I basically want stock driveability, and as much power as possible.

Along with the AFR 205 heads, I have an underdrive pulley, kooks headers and cat back exhaust (standard mufflers though, vararam, ported throttle body and a 78 fast intake (did not go the 90 because apparently these give exactly the same drivability as the LS6 intake).

DCR versus SCR????

RussellNewnham

Was not clear about the 78 fast. Imeant to say that there are allegedly no drivability issues with the 78, where as the 90 can be hard to tune.

TheBlurLS1

iTrader: (8)

DCR = dynamic compression ratio

SCR = static compression ratio


SCR is when you say X amount of cubic inches compressing to Y amount of cubic inches, very easy to calculate.

DCR is when you take into account the SCR and the individual valve events. You now have to consider things like how much is actually being sucked in, how much is actually being exhausted, and how fast. When people say "The cam bleeds off a little compression....", they're talking about DCR.



Since the camshaft effects on these cars seem to be pretty close to the same, unless its some sort of custom job, most people pay most of their attention to the SCR.

slow trap

iTrader: (22)

that should be a good combo with 11:0 cr with a tune you should be fine.

GuitsBoy

iTrader: (4)

Big cubes swallow up compression the same way they swallow up cam duration. In other words, 11.3:1 on a 346 is much higher than 11.3:1 on a 408. Im having ping issues already up in the northeast with 10.85 SCR. I get a ton of part throttle ping on days its warmer than 65*. Ive really had to lower the timing down quite a bit even from stock at part throttle.

SiL3NtXWS6

iTrader: (17)

I ran 11:1 on my 346 with a 224/228 cam before i ran 11:3 on my 408